Analysis & Opinion

(Reuters) - If you're a motorist expecting to get 35 miles per gallon on your new car and you end up only getting 20, the cost difference can add up. At the current national average of $3.94 per gallon of regular unleaded gas, it would cost those with a lower-performing car an extra $1,266 after driving it 15,000 miles, the average distance that Americans travel over the course of a year.

With gas prices so high and many consumers keen on more environmentally friendly motoring choices, it's particularly important to understand what you're buying and how to get the best fuel economy from your car.

The stickers on new-car windows, with the U.S. Environmental Protection Agency's miles-per-gallon estimates, can frustrate consumers who fail to get the mileage the stickers appear to promise. Indeed, motorists may be further encouraged about their car's performance by a recent study which suggests that U.S. new-car gas mileage has risen 20 percent over the past five years.

Though the stickers come with a disclaimer that says, "Your actual mileage will vary," thousands of consumers still descend upon Internet message boards to discuss how the performance of their cars differs from the estimates.

"I figured that this is what you can expect, otherwise, why put it on there? When they put the two numbers there, my brain assumes my mileage will be within that range," says one of those consumers, Mike Pascale, 48, a copywriter and storyboard artist in Modesto, California, who can't remember a car he drove that got the gas mileage that its window sticker said it would.

Car companies often use the mileage estimates generated by the EPA for their advertising efforts, a habit that Carroll Lachnit, feature editor of automotive information firm Edmunds.com, says should be tempered.

"Car companies may be setting themselves up for criticism by using those numbers so prominently in their advertising," Lachnit says. "Consumers seize on numbers - particularly with gas as expensive as it is."

DISAPPOINTMENT

The numbers can lead car buyers down a frustrating path, says George Cook, a former member of Ford Motor Co.'s marketing operation who is now executive professor at the Simon Graduate School of Business at the University of Rochester.

"As a new vehicle purchase criteria, miles per gallon can be a big deal to a consumer," he says. "We believe what we see until we find out differently."

So, is the disappointment the manufacturers' fault? The EPA's? Drivers themselves? Well, as a consumer, you can gripe, sue, or adopt some active measures to increase your gas mileage.

The issue of underperforming cars received heightened attention in February, when Californian Heather Peters won a small-claims judgment against Honda Motor Co. Peters took the company on herself, alleging her 2006 Civic delivered 30 mpg instead of the EPA-estimated 50 mpg. The case has been appealed. (Read a related story here, link.reuters.com/gad67s)

In December, the group Consumer Watchdog took Hyundai Corp. to task for using a 40 mpg reference (its EPA highway mileage rating) in ads for its Elantra and asked the EPA to retest the vehicle due to complaints by consumers.

But Jim Trainor, spokesman for Hyundai Motor America, says that Popular Mechanics magazine did its own testing, which showed the vehicle matched and even surpassed that figure.

VARYING RESULTS

The disparate results highlight the idea that every driver's experience is going to vary, Trainor says.

"If you're (driving) around town and going a mile here, a mile there...you're not going to get anything close to the EPA's test ratings." Understanding that, he says, "is a real public education issue."

The split between EPA mileage estimates and actual performance has spawned a variety of options for consumers to get a better feel for reality - where drivers log in with their actual performance. Among the sites that collect such data are: Fuelly.com, TrueDelta.com, CleanMPG.com and even the EPA's own FuelEconomy.gov.

What Lachnit, Trainor, Cook and others say is that everyone may have a different experience. The weather, vehicle maintenance, and where and how it's driven all factor into the performance of a car.

Driving style alone could cause a 35 percent drop in fuel efficiency, says Lachnit. Someone who weaves in and out of traffic and is heavy-footed on the accelerator will get much lower gas mileage that someone who is slow and steady, she says.

"There are huge variances," confirms Eric Mallia, business manager for FleetCarma in Waterloo, Ontario. "We've done some analysis and seen up to 60 percent variance from window sticker (estimates). We find that's something most people don't understand."